Exact Quench Dynamics from Thermal Pure Quantum States

• URL: http://arxiv.org/abs/2510.05346v2
• Date: Thu, 23 Oct 2025 08:31:09 GMT
• Title: Exact Quench Dynamics from Thermal Pure Quantum States
• Authors: Hui-Huang Chen,
• Abstract summary: We present an exact solution for the real-time dynamics following a quench from a thermal pure quantum (TPQ) state in an integrable system.<n>The approach to equilibrium shows highly nontrivial coherent dynamics.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: We present an exact solution for the real-time dynamics following a quench from a thermal pure quantum (TPQ) state in an integrable system. Although equilibration is expected in this setting because the TPQ state already encodes the thermal expectation values of all conserved quantities, the approach to equilibrium shows highly nontrivial coherent dynamics. In the spin-1/2 XX chain, local observables become stationary at their thermal values after dephasing, while the entanglement entropy exhibits a characteristic double-plateau structure. We obtain this behavior exactly using three complementary approaches: two-dimensional (2D) conformal field theory (CFT) on the Klein bottle, an exact numerical evolution based on the matrix Riccati equation, and an asymptotically exact quasiparticle picture. These results demonstrate that the non-monotonic entanglement evolution is a macroscopic manifestation of the coherent dephasing of anomalous pairing correlations in the initial TPQ state.

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